The present invention relates to a device in a machine-control system and/or process-supervision system operating with the CAN-protocol according to standard ISO 11898. CAN-systems of this type comprise modules which are intercommunicable via a digital serial communication and in which a control and/or supervisory function can be realized from a first module or from a unit, which is communicable with the CAN-system, belonging to one or more second module(s).
The present invention relates to a device in a machine-control system or process-control system. The said system has in the present case been referred to as a CAN-system, since the systems in question are required to use the signal protocol according to CAN (Controller Area Network, corresponding to standard ISO 11898). The invention in this case relates to those types of CAN-system comprising modules which are connectable via a digital serial communication and in which a function in a first module is intended to be able to be observed, stimulated or registered at a location for the placement of the first module. Reference is also made to Swedish patent application “Device in a system operating with CAN-protocol”, which was submitted on the same day by the same applicant and inventor.
It is previously known to be able to control machinery and equipment at control desks which are connected via fixed connections or wireless connections. These proposals make use of the general control and supervision principles. With reference to control desk arrangements proposed with CAN-protocol, the arrangements in question are primarily those with wire connections. Reference is also made to U.S. Pat. No. 5,392,454.
With machine-control and process-control systems of this category, it is previously known that it is necessary to supervise the aggregates served by the modules such that in fault-searching, system design, etc., it is possible to establish whether the equipment controlled by a particular module is behaving as expected. It can be stated in this context that it may be necessary to monitor the functions at valves, thermometers, etc., so that in certain functional states it can be seen or registered whether the components in question are actually performing their expected function. It is also known to utilize machine-control systems and process-control systems in which the equipment parts are connected via relatively long digital serial communications. The connection can also be established at locations and sites where accessibility is limited.
In the radio-controlling of machines operating with CAN-protocol, problems arise from the fact that the protocol calls for arbitration and confirmation functions which are extremely time-critical. In order to ensure that the modules do not misinterpret a particular message in question, in certain cases the receipt of a one over the connection must result, for example, in a zero being immediately presented to prevent disturbances occurring within the system. This calls for sending and receiving to be effected simultaneously by one and the same module, which, in turn, calls for a full duplex connection and time synchronization between the sending and receiving channel in each module and predetermined maximum wave propagation time within the system. This is difficult to achieve in a radio system when such a system is often chosen to enable the distance between the modules within a system which are connected by radio link to be easily varied. Radiocommunication is therefore less suitable for systems using the CAN-protocol. The object of the present invention is to solve these problems.
In certain contexts, it is vital to be able to make use of repetition functions linked to machines or machinery stocks operating with CAN-protocol. At places which are difficult to survey or difficult to access, there is a need to build up an existing CAN-system and introduce a repetition function over difficult stretches or to create on a temporary or longer term basis two separately working CAN-systems instead of one. In this context, there is a need to be able to facilitate system developments and system applications. The object of the invention is to solve these problems also.
There is also a need to achieve effective coordination of machine-controls in machinery stocks, e.g. in weaving sheds in which weaving machines have hitherto been controlled individually and provided with their own man-machine interface such as control desks. There is a wish to be able to introduce CAN-protocol into the control of machines of this category, this having been hindered by the above-specified problems. The object of the present invention is to solve these problems also and it is proposed, in respect of this category of machinery-stock control, that the controls be effected via radiocommunication from and to a common man-machine interface, such as a control unit or control desk. The control equipment, is thereby simplified and a coordinated, effective control is able to be established in terms of service and production via or in the machinery stock.
Radiocommunication is often utilized between an operator's control unit and the control system of the machine which he controls. Examples of such systems are radio-controlled airplanes, radio-controlled contracting machinery, radio-controlled hoisting cranes, etc. of various types. One problem is here to set up a radio channel which is exclusively between control unit and machine, such that the connection is not disturbed by other operator/machine connections. The object of the present invention is to solve this problem also.
The invention also allows reduced susceptibility to theft and offers high security within the system per se.
There is a great need to be able to carry out fault searches and tests on modules which are situated at a distance apart and in which a functional effect upon a first module is wanted to be able to be followed at a second module, and vice versa. For instance, there is a desire in certain situations to initiate controls at a master in the CAN-system in order to obtain manifestations at one or more slave modules. There is here a need to see whether the function is being correctly performed by the components or aggregates controlled by the module in question.
There is also a need to be able to stimulate a component or aggregate at a module and to discover what repercussions this has.
There is also a need to be able to carry out registration operations in a fault-searching and testing context for a certain period, as well as to acquire direct visual and signal information at the site for the module subjected to testing or fault-searching.
The above must be practicable even if the modules are far apart and hidden from each other. Preferably, the above will be able to be effected via an already existing switching function, i.e. connections and disconnections do not need to be made in each separate case/in respect of each module.